Flexible catheter with a drive shaft

ABSTRACT

The invention relates to a flexible catheter (1) with a drive shaft (2), with a sleeve (6) surrounding the drive shaft (2) and with a sheath (7) surrounding the drive shaft (2) and the sleeve (6), wherein the drive shaft, the sleeve (6) and the sheath (7) are pliable, wherein the drive shaft (2) at a proximal end of the drive shaft (2) comprises a coupling element (5) for connecting the drive shaft (2) to a drive motor (18), wherein the drive shaft (2) at least regionally consist of a alloy which contains at least 10% by weight of chromium, nickel and cobalt in each case. The invention moreover relates to a blood pump arrangement with such a catheter.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/033,443, filed Apr. 29, 2016, which is a U.S. National Stage filingunder 35 U.S.C. § 371 of International Application No.PCT/EP2014/073504, filed Oct. 31, 2014, which claims priority toEuropean Patent Application No. 13191307.1, filed Nov. 1, 2013, thecontents of all of which are hereby incorporated by reference herein intheir entirety. International Application No. PCT/EP2014/073504 waspublished under PCT Article 21(2) in German.

The invention relates to a flexible catheter with a pliable drive shaft,according to the preamble of the main claim, as well as to a blood pumparrangement with such a catheter.

Such catheters are typically used, within a body of a human or animal,to produce or transmit a torque or rotation movement. The drive shaftruns axially along the longitudinal extension of the catheter between aproximal end of the catheter and a distance end of the catheter.Typically, a proximal end of the drive shaft is connected outside thebody to a drive motor, in order to produce the torque or the rotationmovement and to transmit it onto the drive shaft. A rotation element orfunctional element which is designed according to the respectiveapplication is connected to the drive shaft in a rotational fixedmanner, at the distal end of the drive shaft. With regard to thefunctional element, it can be the case for example of a milling cutter,a rotor ablator or a pump rotor for delivering blood.

For many applications, it is necessary to lead the catheter along adesired path through the body, for example along or within bloodvessels, in order to position the distal end of the catheter at adesired location within the body, for example within a heart ventricle,for the duration of the respective application. Apart from thepliability and flexibility which is necessary for this, as a rule yetfurther criteria must be fulfilled. For example, in some applications,it is necessary for rotation movements to be produced or transmitted bythe drive shaft at a very high rotation speed, for example the necessaryrotation speed can be more than 10,000, more that 20,000 or even morethan 30,000 revolutions per minute, such as in the already mentionedcase of delivering blood for example. Moreover, particularly highdemands are placed on the mechanical and the chemical loadability of thecatheter, particularly at the drive shaft, in cases, in which therotation movement must be produced over a longer period of time, thusfor several hours, days or even weeks, as is can likewise whendelivering (pumping) blood. Material fatigue and damaging processes onthe drive shaft and on other components of the catheter should onlyprogress as slowly as possible, and moreover as predictably and ascontrollably as possible. Tearing and breakage of the drive shaft onoperation should be able to be ruled out with an as large as possiblecertainty in critical applications, such as when delivering blood.Hereby, it is not favourable if the flexible drive shaft is operated ina sheath which is too hard and which wears the shaft.

On the other hand, should a failure of the shaft occur despite this,then it must be ensured with the greatest possible certainly that theends of the shaft which are thereby typically splayed open, do not workthrough the sheath of the catheter usually consisting of plastics, athigh speed. The ends of the shaft would freely rotate in the bloodvessel in such a case.

It is thus the object of the present invention, to suggest a flexiblecatheter with a pliable drive shaft and which is as reliable is possibleand is also suited as much as possible for a permanent operation at highspeeds. A blood pump arrangement is moreover suggested, which islikewise as reliable as possible and is as suited as much as possiblealso for the permanent operation at high speeds.

This object is achieved by a catheter according to the main claim, aswell as by a catheter and a blood pump arrangement according to theauxiliary claims. Preferred embodiments and further developments are tobe deduced from the dependent claims.

As is described hereinafter in a detailed manner, this patentapplication discloses several aspects, wherein each of these aspects isa part of a coherent invention. On the other hand, each of the aspectsalso per se already represents an autonomous invention. The aspects cantherefore be realised independently of one another (and in each casetaken by themselves represent special further developments of a genericcatheter according to the preamble of the main claim)) and can moreoverbe infinitely combined with one another, in order to synergisticallyimprove a generic catheter or a blood pump arrangement with a genericcatheter. Thus for example a generic catheter can be designed accordingto one of these aspects and can simultaneously also be designedaccording to one (or more) further aspect(s). This catheter is then aparticularly advantageous embodiment of a catheter according to thefirst mentioned aspect. Each of the aspects thus also permits a furtherdevelopment of each other aspect.

The first of these aspects relates to the material or the materialcharacteristics of the drive shaft, the second aspect to the geometricdesign of the drive shaft, the third aspect to the design of the sleeve,the fourth aspect to the connection between the drive shaft and thedrive motor, the fifth aspect to the mounting of the drive shaft and thesixth aspect to a lubricant for the drive shaft. Each of these aspectscontributes to the improvement of the loadability and the reliability ofthe catheter or of the blood pump arrangement.

A generic flexible catheter accordingly comprises a drive shaft, asleeve surrounding the drive shaft and a sheath surrounding the driveshaft and the sleeve, wherein the drive shaft, the sleeve and the sheathare pliable. The drive shaft at a proximal end of the drive shaftcomprises a coupling element or a coupling head, for the connection ofthe drive shaft to the drive motor.

Typically, the (axial) total length of the catheter is between 50 cm and200 cm, and as a rule the total length lies in a region between 80 cmand 150 cm. Typically, the (axial) total lengths of the drive shaft, thesleeve and the sheath likewise lie within of one these regions in eachcase. The flexibility or the pliability of the catheter, thus inparticular of the drive shaft, the sleeve and the sheath, should besufficient, in order to be able to elastically bend the catheter with aradius of curvature in a region between 20 mm and 40 mm, preferably in aregion between 25 mm and 35 mm, in particular of about 30 mm. With sucha curvature, in particular the drive shaft rotating at an operationalspeed and the sleeve, where possible, should deform only elastically,thus if possible, no permanent (plastic) deformations or changes of thedrive shaft or the sleeve should occur. In particular such an elasticcurvature with the mentioned radius of curvature should also be possiblewith a roughly U-shaped curvature of the catheter of about 180°, withwhich the catheter therefore is continuously curved, for example alongan axial section of the catheter with a length of about 80 mm to 150 mm,typically 100 mm to 120 mm (depending on the radius of curvature). Suchcurvatures of the catheter occur for example if the catheter runsthrough the aortic arch into the left ventricle. Moreover, a rhythmicchange of the described radius of curvature typically occurs due to therhythmic heart action, wherein the position of the curvature withrespect to the catheter can also rhythmically change.

In many cases, it is not necessary for the catheter to have such aflexibility along its entire axial longitudinal extension. It canalready be sufficient for this to be given in a certain axial section(or several axial sections). Often, at least a distal end-piece or adistal part-piece of the catheter has such a flexibility, as in the caseof delivering blood, for example if a distal end of the catheter has tobe placed in a ventricle. This distal end-piece or part-piece forexample can have an axial length in one of the length regions mentionedabove.

As is described in more detail further below, the pliability andflexibility of the catheter or the drive shaft also cannot be too largein some cases, in particular in those axial sections of the drive shaft,which run distally or proximally outside the sleeve or exit out of thesleeve, so that a regional stiffening of the drive shaft to a certainextent is advantageous in at least one of these sections, or, dependingon the demands of the respective application, can even be necessary. Aminimisation of the vibration can advantageously be achieved by suchstiffening, by which means the risk of a haemolysis can also be reduced.

According to the first aspect of the invention, the drive shaft of thecatheter can consist completely or at least regionally of an alloy whichin each case contains at least 10% by weight of chromium, nickel andcobalt. The alloy preferably contains at least 30% by weight of nickel,preferably however not more than 40% by weight of nickel. The alloypreferably contains at least 30% by weight of cobalt, preferably howevernot more than 40% by weight of cobalt. The alloy preferably contains atleast 15% by weight of chromium, preferably however not more than 25% byweight of chromium. The alloy preferably also contains molybdenum,preferably at least 5% by weight, preferably however not more than 15%by weight of molybdenum.

The alloy for example as alloy components can comprise about 35% byweight of nickel, about 35% by weight of cobalt, about 20% by weight ofchromium and about 10% by weight of molybdenum. These alloy componentsof the alloy in each case can be larger or smaller by up to 3% byweight, or larger or smaller by in each case up to 2% by weight. Thealloy components of these elements can correspond to the alloycomponents of these elements in the alloy MP35N® or the alloy componentsof these elements in the alloy 35 NLT® or differ from this in each caseby up to 2% by weight higher or lower, or from this in each case by upto 1% higher or lower. The alloy can moreover contain further alloyelements. These can be selected and weighted according to those of thealloy MP35N® or those of the alloy 35NLT®.

Preferably, with regard to the alloy it is the case of MP35N® or 35NLT®,or is manufactured in a corresponding (or the same) manner, i.e. withcorresponding (or the same) method steps and with corresponding (or thesame) method parameters as MP35N® or as 35 NLT®. For example, one canenvisage the alloy of the drive shaft or the drive shaft as a wholebeing work-hardened or being manufactured or formed by way of applying(high) cold-forming or work-hardening. A work-hardening degree of thematerial of the drive shaft and/or of the sleeve for example is between35% and 70% and/or between 40% and 60%. A tensile strength of thematerial in a region between 1900 MPa and 2200 MPa can result from this.

The relations between the yield point, tensile strength, elongation atbreak and work-hardening degree with the example of the material 35NLTis represented by way of example in FIGS. 16 and 17 (based on thedetails of the manufacturer Fort Wayne Metals). With this example, it isshown that different heat-treatment conditions and work-hardeningdegrees of a material can generally lead to very different materialcharacteristics. Often, these are only found to be unsuitable for aflexible drive shaft with the benefit of hindsight.

A high work-hardening for example is not uncritical, since this can leadto a reduction of the maximal elongation at break as well as thetoughness of the material. The reverse bending strength of the driveshaft as well as the achievable bending radius of the shaft can benegatively influenced by way of this. On the other hand, a lowwork-hardening entails a relative low harness and tensile strength ofthe material. A hardness which is to low has a direct influence on thewearing behaviour of the shaft and thus on its endurance strength, andfor example can result in an increased wear and abrasion on operation.This is particularly critical in the case of a sliding/friction pairing,as is typical for flexible shafts. A reduced tensile strength results ina low reverse bending strength.

The optimisation of a stable and durable flexible drive shaft is highlycomplex since different optimisation targets of the drive shaft entaildiverging material characteristics, so that no standardised andmeaningfully applicable optimisation method or evident parameter windowresult for this.

However, it has been surprisingly found that drive shafts which consistcompletely or at least regionally of a material which has a tensilestrength in a region between 1800 N/mm² and 2400 N/mm², preferably from2034 to 2241 N/mm² (thus from 295 KSI to 325 KSI), lead to good results.In particular, with regard to the material, it can be the case of one ofthe alloys described here, thus one which comprises at least 10% byweight of chromium, nickel and cobalt in each case. However, othermaterials are also considered for the drive shaft, apart from thesealloys, such as for example metallic and non-metallic materials, inparticular also plastics and composite materials.

A drive shaft which consists completely or at least regionally of suchan alloy or such a material is also suitable for applications at a veryhigh speeds and a long permanent operation, so that it is also possibleto maintain the initially mentioned speed regions for a longer timeduration with such a drive shaft. The torques, which transmit such highrotation speed by way of the drive shaft however are typicallyrelatively low, in particular when delivering blood, wherein the torquefor the drive of an expanded pump rotor is typically larger due to thelarger diameter. Even if the application of the alloys MP35N® or 35NLT®may be known for different medical instruments such a stylet forexample, due to their loadability and their corrosion resistance, theirsuitability for pliable drive shafts however is surprising due to thedescribed special demands, in particularly at a high speed, longoperational duration and large curvature, in particular in light of thefact that indeed more than 500 000 000 complete load reversals and inextreme cases more than 1 000 000 000 load reversals can occur with theapplication as a blood pump.

Alloys with a relatively high iron content or titanium content have beenapplied until now for the drive shaft, in particular for blood pumps, inorder to achieve a high loadability. However, as has been found withinthe framework of the present invention, one can or indeed one shouldmake do without a high content of iron and titanium as much as possible,in order to permit permanent operation as high rotation speeds. Theweight component of iron and titanium is even preferably selectedrelative low, for example in each case less that 2% by weight or evenless than 1% by weight. Basically, one can completely make do withoutiron and titanium as alloy components, corresponding to weight componentof less than 0.1% in each case.

According to a first aspect, the drive shaft can consist completely orat least regionally of an alloy which has a weight component of ironwhich is less that 2% or preferably less that 1% or particularlypreferably less than 0.1%. According to the first aspect, the driveshaft can consist completely or at least regionally of an alloy whichhas a weight component of titanium which is less that 2% or preferablyless than 1% or particularly preferably less than 0.1%.

The drive shalt, the sleeve, the sheath and/or bearing elements whichare present as the case may be, consist as much as possible ofbiocompatible materials, or at least outer surfaces of the respectivecomponents consist of a biocompatible material.

According to the second aspect of the invention, the drive shaft cancomprise a cavity extending axially within the drive shaft. With regardto the drive shaft, it can therefore be the case of a hollow shaft. Thecavity can extend within the drive shaft along a complete longitudinalextension of the drive shaft. A high pliability of the drive shaft witha simultaneously relatively large torsional stiffness can be achieved bysuch a cavity. The pliability can be increased further if the driveshaft comprises a plurality or a multitude of coaxial windings which runspirally around the cavity of the drive shaft. Torsion and bendingstresses can moreover be converted into axial tensile or compressivestresses by way of the windings, by which means the loading of the driveshaft can be reduced. Moreover, it is also possible for the windings ofthe drive shaft to be arranged in two or more coaxial layers of thedrive shaft. The windings within different coaxial layers thenpreferably have opposite winding directions. Tensile and compressivestresses between the layers and which are caused by torsion stresses canthen be completely or partly mutually compensated in this manner. As awhole, bending stresses in the drive shaft can therefore also bereduced.

With regard to the windings of the drive shaft, it is typically the caseof windings of a wound wire or several corresponding wound wires. Thedrive shaft can comprise exactly one or several such wires within eachlayer, for example 1 to 8 wires, preferably 4 to 6 wires, particularlypreferably 5 wires. The wire or the wires preferably consist of thealloy which is described above. The wire or the wires typically in eachcase have a diameter in a range of about 0.09 mm to about 0.21 mm,preferably of about 0.135 mm to about 0.165 mm. An outer diameter of thedrive shaft typically lies in a range of about 0.53 mm to about 1.32 mm,preferably in a range of about 0.79 mm to about 0.97 mm. Outer diametersof the drive shaft below 1 mm are particularly preferred. An innerdiameter of the drive shaft typically lies in a range of about 0.17 mmto about 0.39 mm, preferably in a range of 0.25 mm to about 0.31 mm.Axially adjacent windings of the inner layer mutually contact in thecase of two concentric layers, whereas axially adjacent windings of theouter layer preferably do not mutually contact (in each case given analignment of the drive shaft free of curvature), but have an axialdistance in a range of about 0.018 mm to about 0.042 mm, preferably ofabout 0.027 mm to about 0.033 mm.

A small outer diameter of the catheter can also be realised by a smallouter diameter of the drive shaft, by which means a reducedtraumatisation of the tissue at the location of puncture can beachieved. Further advantages which can be achieved by a low outerdiameter of the drive shaft are lower friction and wear problems due toa reduced peripheral speed of the drive shaft, lower vibration problemsdue to a reduced mass of the drive shaft, as well as reduceddisturbance/interference of motor current signals due to vibrationswhich result from this, and for example a reduced danger of possiblypresent calcifications within the blood vessel detaching from the vesselwall and possibly getting into the circulation with possiblylife-threatening consequences for the patient.

Surprising, it has thus been found that the transmission of adequatelyhigh torques, for example for driving an expandable pump rotor in theexpanded condition, are also possible with the low outer diameters ofthe drive shaft of less than 1 mm which are mentioned here, over alonger period. Hereby, in particular the special ranges of the diameterof the wires and which are specified above have been found to beparticularly advantageous in the case of a shaft constructed of suchwires, wherein it has moreover been found that the optimal region forthe diameter of the individual wires is related to the outer diameter ofthe drive shaft in a non-trivial manner.

Moreover, one can envisage the windings of the drive shaft beingmanufactured or formed by way of a (high) cold-forming orwork-hardening, in order to improve the elasticity and endurance of thedrive shaft.

It is possible for the cavity to be filled out with a reinforcementmaterial, completely or within axial sections of the drive shaft, inorder to set the stiffness and stability of the drive shaft in therespective axial section and increase it (regionally as the case maybe). As already explained in the context of the first aspect of theinvention, apart from a sufficient pliability of the drive shaft, anadequate stiffness of the drive shaft is also necessary for a reliableoperation of the catheter, in particular at high speeds and longeroperational duration, for example in order to permit a stable rotationof the drive shaft, in particular in axial sections of the drive shaftwhich run distally or proximally outside the sleeve (distal and proximalend-piece of the drive shaft restively). The first and the second aspectof the invention synergistically complement one another in this manner.In a preferred embodiment, one accordingly envisages a distal end-pieceof the drive shaft and/or a proximal end or end-piece of the drive shaftbeing stiffened. The stiffened distal or proximal end or the end-piecepreferably has a length between 10 mm to 60 mm, particularly preferablya length between 20 mm and 50 mm. The drive shaft is preferablystiffened in those regions, in which (additionally to the sleeve orinstead of it, which is to say in place of the sleeve) bearing elementsare arranged for the axial and/or radial mounting of the drive shaft.Moreover, it can also be advantageous to stiffen the drive shaft in theregion, in which the drive shaft proximally enters or exits the sleeveand as a result is not guided in the sleeve. Moreover, it can also beadvantageous to stiffen the drive shaft in the region, in which thedrive shaft enters or exits the sleeve distally. It is indeed in thesetransition regions that bending loads or other loads, such asoscillation load for example, of the drive shaft, can be reduced by wayof a stiffening of the drive shaft.

Materials which are characterised on the one hand by a high stiffnessand simultaneously by a relatively high elastic deformability on theother hand are suitable as reinforcement materials for stiffening thedrive shaft. In particular, the reinforcement material or the stiffeningmaterial should tolerate all bending, to which the catheter or the pumphead of the catheter is subjected to during the implantation and duringoperation. A non-rusting, austenitic steel for example is considered asa reinforcement material, for example a steel according to the materialnumber DIN 1.4310.

Alternatively or additionally to the described reinforcement material, asuitable stiffening can also be achieved by way of (axial and/or radial)welding or soldering of (axially or radially) adjacent ones of thewinnings of the (spiral) drive shaft. Moreover, it is also possible fora certain (and under certain circumstances sufficient) stiffening of thedrive shaft to be able to be achieved by way of the distal functionalmodule which is typically fastened on an outer periphery of the driveshaft in a rotationally fixed manner, such as a pump rotor.

According to a third aspect of the invention, the sleeve can be designedas a bearing coil with a plurality of windings. The windings of thebearing coil run around the drive shaft in the axial direction in themanner of a spiral. The bearing coil for example can be a wound flattape. The flat tape preferably has a width (measured axially) which islarger than the thickness (measured radially) by a factor of at least 3,preferably by factor of 6. Typically, the width of the windings lies ina range of about 0.36 mm to about 0.84 mm, preferably in a range ofabout 0.54 mm to about 0.66 mm. The thickness of the windings typicallylies in a range of about 0.06 to about 0.14 mm, preferably in a range ofabout 0.09 mm to about 011 mm. An inner diameter of the sleeve typicallylies in a region between about 0.6 mm and about 1.4 mm, preferably in arange of about 0.9 mm to about 1.1 mm. An outer diameter of the sleevetypically lies in a range of about 0.72 mm to about 1.68 mm, preferablyin a range of about 1.08 mm to about 1.32 mm. A pitch of the bearingcoil preferably lies in a range of about 0.43 to about 0.98, preferablyin a range of about 0.63 to 0.77, wherein the inner diameter of thesleeve corresponds to the outer diameter of the flexible drive shaft, inparticular is larger than the outer diameter of the drive shaft.

The bearing coil, in the case that it is designed as a wound flat tape,has low as possible manufacturing tolerances with respect to an (axial)tilting of the windings relative to the longitudinal axis of the bearingcoil (in the straight condition without curvature of the bearing coil).The tilting is preferably less than 10°, in particular preferably lessthan 5°. The inner surface of the sleeve or of the windings of thebearing coils therefore preferably forms cylinder-shaped part-surfacesinstead of conical part-surfaces (tilting). A tilting of the windings tothe longitudinal axis leads to a reduction of the available bearingsurface and to a greater pressure loading of the drive shaft. Thelateral edges of the flat tape are preferably rounded as much aspossible, in order to avoid pressure peaks upon the drive shaft as muchas possible. The radius of curvature of the edges is preferably 0.04 mmor more.

The sleeve can consist completely or at least regionally of an alloy.The description of the alloy of the drive shaft can accordingly also beconferred upon the alloy of the sleeve. In particular, the sleeve cancompletely or at least regionally consist of the same material, forexample of the same alloy as the drive shaft.

In a laboratory test, very nod results could be achieved in the fatiguetest with the use of the same material for the drive shaft and thesleeve, under a different pulsatile load and with bending radiisignificantly below 50 mm. This is surprising in many aspects. Forexample, specifically for reason of patient safety, it is recommended todesign the flexible shaft of a wear-resistant material which isrelatively hard in comparison to the drive shaft, in order, for examplein the case of a shaft breakage which usually leads to a splicing of theshaft in the breakage region, to prevent the drive shaft from rubbingthrough the sleeve and the even softer sheath of the catheter insubsequent operation, and the rotating openly in the blood vessel.Moreover, in classical engineering, the use of equal materials assliding partners or friction partners is usually discouraged, since inthis case a so-called “eating” or corroding of the work-pieces canoccur, which originates from the fact that individual molecules of thetwo sliding/friction partners connect to one another and can then betorn out of the molecular interconnection of the other part. The factthat it is very difficult or impossible to predict which of the twoparts wears is thereby seen as being particularly critical. The use ofthe same materials for a rapidly rotating flexible shaft and a bearingcoil located around this, which is suggested here, is thereforesurprising to the man skilled in the art.

The fourth aspect of the invention relates to the design of the proximalcoupling element or coupling head of the drive shaft which surprisinglycan likewise significantly improve the reliability of the catheter andits suitability for permanent application, in particular if this aspectis combined with one of the other aspects. The basic idea of the fourthaspect lies in being able to often significantly reduce the axialcompressive and tensile stresses in the drive shaft if the connectionbetween the coupling element of the drive shaft which itself is as rigidas possible and which is connected to the drive shaft in a rotationally,tractionally and compressively fixed manner, and a coupling element ofthe drive motor which corresponds to this, although being rotationallyfixed, however compensation movements between the coupling element ofthe drive shaft and the coupling element of the drive motor are possiblein the axial direction. For this, the coupling elements of the driveshaft and the drive motor can comprise axial sliding surfaces whichcorrespond to one another and which typically run parallel to the(local) rotation axis or the longitudinal axis of the respectivecoupling element. The shape of these axial sliding surfaces or theirouter or inner contour therefore does not change in the axial direction(thus along the rotation axis or longitudinal axis). The couplingelement of the drive shaft for example can have the shape of a square[end] or of another profile piece, which has a cross-sectional area(defined perpendicularly to the rotation axis or longitudinal axis) orouter contour, which is constant in the axial direction, thus along itslongitudinal extension or rotation axis. The coupling element of thedrive motor can accordingly be designed as a correspondingly designedreceiver for the square end or the profile piece.

As already mentioned, the catheter at a distal end of the drive shaftcan comprise a pump rotor, for example for delivering blood, Which isfixedly connected to the drive shaft. The pump rotor, depending on theconfiguration, design and the pitch angle of the blading of the pumprotor, can be configured for example for the proximal delivery in theblood (proximal delivery direction, i.e. in the direction of theproximal end of the catheter) or for the distal delivery (distaldelivery direction, i.e. in the direction of the distal end of thecatheter). The fifth aspect of the invention relates to an axialmounting of the pump rotor, with which a thrust bearing of the catheteris matched to the delivery direction of the pump rotor such that axialbearing forces primarily or exclusively act upon the drive shaft asaxial tension (pull) forces (and to a lesser extent or not at all asaxial compressive forces). The loading of the drive shaft, particularlyat high speeds can be surprisingly significantly reduced by way of this.Moreover, astonishingly, it has been found that the damage to the blooddue to the pump operation is lower with such a design of the blood pump.Hereby, in the case of a proximal delivery direction, one envisagesarranging the thrust hearing proximally to the pump rotor and beingdesigned to counteract a distally directed axial displacement of thedrive shaft (caused by the proximal delivery effect of the pump rotor).The thrust bearing is arranged distally to the pump rotor and isdesigned to counteract a proximally directed axial displacement of thedrive shaft, in the case of a distal delivery direction.

The thrust bearing for example can comprise a first thrust bearingelement and a second thrust bearing element, wherein the first thrustbearing element is connected to the drive shaft in a rotationally fixedmanner, and the second thrust bearing element is fixedly connected tothe sleeve or to the sheath. The first thrust bearing element and thesecond thrust bearing element comprise sliding surfaces (which can alsobe indicated as abutment surfaces or end-faces) which face one another,are preferably annular and which block an axial displacement of thedrive shaft in at least one direction in the case of a mutual contact.The mentioned sliding surfaces thus overlap one another in the radialdirection. The first thrust bearing element can be designed as a radialwidening of the drive shaft, but also as a ring which is fastened on thedrive shaft, by way of crimping for example. With regard to the secondthrust bearing element, it can simultaneously be the case of a radialbearing element, for example with a sliding surface which faces thedrive shaft, is preferably designed in a cylindrical manner and isarranged coaxially to the rotation axis of the drive shaft.

Preferably, at least one of the mentioned sliding or abutment surfaces,preferably at least the sliding surface of the first bearing element ofthe thrust bearing has a profiling such that the two sliding surfaceswith an interaction with a (fluid) lubricant form an hydrodynamic plainbearing. The lubricant which is described further below is preferablyapplied as a lubricant. The profiling has the function of producing bowwaves or pressure waves of the lubricant between the two slidingsurfaces, wherein these waves run around the drive shaft on rotationaloperation. This design of the sliding surfaces could surprisingly reducethe arising wear in this region by more than 50%.

The profiling of the respective sliding surface for example canpreferably comprise 6 to 24 prominences and/or recesses, whichpreferably in each case can have a height or depth of about 0.03 mm toabout 0.1 mm. Typically, the prominences and/or recesses can be arrangedover this sliding surface in a manner distributed uniformly along aperipheral direction or the circumferential direction of the respectivesliding surface. The prominences can be the same, just as the recessescan be the same. The prominences can be laterally adjacent the recessesand vice versa. In particular, the profiling can be designed as asequence of prominences and/or recesses which alternates (along aperipheral direction). The prominences and/or recesses for example canbe designed as ribs and grooves respectively, which typically, departingfrom an inner edge of the sliding surface which faces the drive shaft,extend in the direction of an outer edge of the sliding surface which isaway from the drive shaft. Typically, the grooves or ribs run preciselyfrom the inner edge to exactly the outer edge and thus therefore have alength which corresponds to the radially measured width of therespective sliding surface.

The ribs or the grooves typically have a width (measured in theperipheral direction) in a range of about 0.08 mm to about 0.5 mm. Thewidth of the ribs or grooves can be constant, or can change in theradial direction. Typically, the profiling along the peripheraldirection of the sliding surface comprises alternating recesses orgrooves and prominences or ribs. If the grooves then have a constantwidth, the ribs then typically widen radially outwards. Such embodimentscan often be particularly simply manufactured by way of milling. On theother hand, if the ribs have a constant with, then the grooves typicallywiden radial outwards. However, it is also possible for the ribs as wellas the grooves to widen radially outwards. The last embodiment can bemanufactured particularly simply by way of laser cutting. The grooves orribs can also be designed spirally in regions, thus extend from theinner edge to the outer edge of the sliding surface, on an arcuate path(for example a circular path).

The catheter can comprise the bearing elements mentioned above, as wellas further bearing elements for the radial and/or axial mounting of thedrive shaft. Zirconium oxide (ZrO₂, also called zirconium dioxide,zirconia), in particular zirconium oxide stabilised with yttrium,aluminium oxide (AlO_(x), typically Al₂O₃), ceramics as well as alloysdescribed in the context of the first aspect are considered in each caseas materials for the bearing elements for example.

According to a sixth aspect of the invention, a cavity or intermediategap between the drive shaft and the sleeve is filled out with alubricant which is biocompatible and preferably also physiological. Withregard to this lubricant, it can be the case for example of distilledwater or an aqueous solution, for example a saline solution and/or aglucose solution. The solution can have a concentration of common saltwhich is physiological, which is to say is 0.9%. However, an isotonicsaline solution or so-called Ringer's solution can also be envisaged. Onthe one hand, the construction of the catheter can be simplified due tothe fact that the lubricant is biocompatible, since an exit of thelubricant into the body does not have to be avoided at all costs.Inasmuch as the materials suggested here are used for the drive shaft,the sleeve and the bearing elements, these components are chemicallyrelatively stable with regard to corrosion by way of these (relativelycorrosive) lubricants, so that the application of these lubricantspractically does not compromise the reliability and suitability of thecatheter for permanent operation. The use of saline solution isparticularly advantageous inasmuch as such a solution as a rule is welltolerated by the patient and has no side-effects, in particular evenwith the presence of a diabetic disease of the patient.

The blood pump arrangement which is suggested here comprises a catheterof the type suggested here, as well as a drive motor for producing arotational movement or torque. A rotationally fixed and preferablyaxially displaceable connection exists between the drive motor or thealready described coupling element of the drive motor, and the couplingelement or coupling head of the drive shaft. With regard to the latter,the description concerning this and in the context of the fourth aspectis referred to. The drive motor can be designed to produce high rotationspeeds, for example rotation speeds in a region between 10,000 and40,000 revolutions per minute. The functional element which is connectedto the distal end-piece of the drive shaft in a rotationally fixedmanner is designed as a pump rotor. The catheter at its distal endcomprises a pump casing, in which the pump rotor is arranged. The pumpcasing for example can be designed in a manner such that the pump casing(for example Whilst being subjected to a (tensile) force acting towardsthe proximal (or distal) end of the catheter), can be brought from anexpanded (or compressed) condition into a compressed (or expanded)condition. The document EP2399639 A1 is referred to concerning thedetails. With a use of a pump arrangement, one can for example envisagethe catheter with its distal end in front being pushed through thefemoral artery via the aortic arch into the left ventricle of the heart,and the pump casing remaining in the left ventricle. A downstream tubingwhich is proximally connected to the pump casing and which thentypically runs through the aortic valves, can for example lead the bloodwhich is driven by the pump rotor and which flows out of the pumpcasing, into the aorta. The proximal end of the catheter and inparticular of the drive shaft, as well as the drive motor is arrangedoutside the body.

With these and similar applications, various external force effects andreverse bending loads act upon the drive shaft and, as the case may be,upon bearing elements of the catheter or of the blood pump arrangement.External force effects and reverse bending loads can be transmitted ontothe catheter, for example by an inner wall of the heart, on which thecatheter bears or is supported as the case may be (for example via aso-called pigtail tip), by way of pulsatile pressure changes or flowchanges of the blood with a ventricle or a blood vessel, for example theleft or right ventricle or the aorta, by way of a positional or attitudechange of the body, in particular by an abdominal movement or a (leg)movement in the proximity of the puncture location. Despite thisloading, blood can be delivered over longer time periods, for exampleover hours, days or even weeks at high rotation speeds of the pumprotor, for example in the mentioned speed range, such as in theapplication in of the blood pump arrangement which is described above,with the suggested catheter and the suggested blood pump arrangement.

As is to be deduced for example from “The Stemotomy Hemopump. A secondgeneration intraarterial ventricular assist device” Wampler R K et al.,ASAIO J. 1993 July-sep;39(3):M218-23, shall breakages in the laboratoryas a rule can only be realistically simulated under pulsatilecompressive loads and bending radii under 2 inches (less than 50.8 mm).The significance of a multiple loading of the shaft is manifested by wayof this. Apart from the pump arrangement suggested here, no pumps with aflexible shaft and which have been successfully applied under pulsatileload in the aortic arch over a longer time are known to the applicant.This is due to the processing of the problem of the flexible shaft,which to this date has not been successful. Moreover, until now, inparticular in the above-mentioned publication of Wampler the al., theuse of a 3-layered shaft instead of a 2-layered shaft was seen as beingessential for improving the service life of the flexible shaft. Thedrive shafts which are suggested here, in contrast have a comparablylong or even yet considerably longer durability and loadability at smallbending radii (smaller than 50 mm) and a pulsatile loading, thanconventional drive shafts, even with a 2-layered design, and thus inembodiments with a significantly smaller diameter than conventionaldrive shafts.

An outer surface of the drive shaft can surprisingly have a relativelyhigh roughness RZ. The roughness RZ for example can lie in a range of0.01 μm to 1 μm, preferably in a range of 0.1 μm to 0.8 μm. Theroughness RZ for example can be about 0.6 μm. The fact that very goodresults could be achieved in the endurance test with a relatively highroughness of the surface of the drive shaft is quiet surprising, sincedue to theoretic considerations, normally an as smooth as possiblesurface would be preferred, in order to minimise wear due to friction,in particular if a relatively corrosive substance, such as physiologicalsaline solution or glucose solution is used as a lubricant as issuggested here, which with regard to its lubricative effect does noteven come close to lubricants common in industry, so that the designprinciples which are usually applicable to classic engineering evidentlycannot be directly conferred even with respect to this.

As already described, a flexible catheter of the type suggested herecomprises a drive shaft, a sleeve surrounding the drive shaft and asheath which surroundings the drive shaft and the sleeve, wherein thedrive shaft, the sleeve and the sheath are pliable, wherein the driveshaft at a proximal end of the drive shaft comprises a coupling elementfor connecting the drive shaft to a drive motor.

The drive shaft moreover can comprise an outer diameter of less than 1mm. The drive shaft and/or the sleeve, at least regionally preferablyconsists of a material which has a tensile strength between 1800 N/mm²and 2400 N/mm², preferably between 2034 N/mm² and 2241 N/mm². The driveshaft and/or the sleeve at least regionally can consist of anon-metallic or a metallic material. In the case of a metallic material,it is hereby preferably the case of an alloy as already describedfurther above, which thus contains in each case at least 10% by weightof chromium, nickel and cobalt. This alloy can have the features alreadydescribed above. The drive shaft and the sleeve cart completely or atleast regionally consist of the same material. Moreover, as has alreadybeen described further above, a surface of the drive shaft can have aroughness of between 0.01 μm and 1 μm, preferably between 0.1 μm and 0.8μm, Of course, the catheter can have all of the features and featurecombinations, which have been described beforehand and are describedhereinafter.

The mentioned aspects of the present invention are hereinafter explainedin more detail by way of a special embodiment example of a catheter ofthe type suggested here and of a blood pump arrangement of the typesuggested here, which are represented schematically in FIGS. 1 to 16,There are shown in:

FIG. 1 a catheter of the type suggested here, in a lateral view,

FIG. 2 a blood pump arrangement with the catheter shown in FIG. 1, in animplanted condition,

FIG. 3 axial sections of parts of the drive shaft of the catheter ofFIG. 1, in a lateral view,

FIG. 4 a cross section through the drive shaft which is represented inFIG. 3, at the location which is characterised there at AA,

FIG. 5 a distal end-piece of the drive shaft which is stiffened with areinforcement material, in a lateral view,

FIG. 6 a longitudinal section through the end-piece which is shown inFIG. 5, at the location which is characterised there at AA,

FIG. 7 a sleeve of the catheter which is shown in FIG. 1, in a lateralview,

FIG. 8 a cross section through a part-region of the sleeve shown in FIG.7 said part region being characterised there at A,

FIG. 9 a longitudinal section through the catheter which is shown inFIG. 1, in the axial part-section which is characterised there at Y,

FIG. 10 the distal end-piece which is represented in FIGS. 5 and 6, witha pump rotor which is fastened on this in a rotationally fixed manner,

FIG. 11 a longitudinal section through the catheter which is show inFIG. 1, in the axial part-section which is characterised there at Z,

FIG. 12 a longitudinal section through a coupling module of the catheterwhich is shown in FIG. 1, and

FIG. 13 an embodiment example of a bearing element of an thrust bearingshown in FIG. 9, in a perspective representation,

FIG. 14 a further embodiment example of the hearing element which isshown in FIG. 13, likewise in a perspective representation,

FIG. 15 readings of yield point, tensile strength and elongation atbreak, for different values of the work-hardening degree for thematerial 35NLT®, and

FIG. 16 diagrammatic representation of the readings of tensile strengthand elongation at break, which are specified in FIG. 15, as functions ofthe work-hardening degree for the material 35NLT®.

Recurring features or features which correspond to one another arecharacterised by the same reference numerals in the figures.

A special embodiment of a flexible catheter 1 of the type suggested hereis represented schematically in FIG. 1. The catheter 1 comprises apliable drive shaft 2, of which in this figure a proximal end-piece 3 isto be seen, said end-piece projecting out of a proximal coupling module4 (cantilever), and at its proximal end the drive shaft 2 comprises acoupling element 5 for the connection of the drive shaft 2 to a drivemotor, cf. FIG. 2. The catheter 1 moreover comprises a pliable sleeve 6(not shown here, but see FIGS. 7 to 9) which surrounds the drive shaft 2and radially mounts it, and a pliable sheath 7 surrounding the driveshaft 1 and the sleeve 6. Thus whereas the coupling module 4 and theproximal end-piece 3 of the drive shaft 2 are arranged at a proximal end8 of the catheter 1, the catheter 1 at a distal end 9 of the catheter 1comprises a pump head 10 with a pump casing 11, with a terminatinghousing 13 which is arranged distally to the pump casing 11 and is fordrive shaft 2, and a downstream tubing 12 which is proximally adjacentthe pump casing 11 (elements running within the downstream tubing 12 arerepresented dashed in FIG. 1). A support element 14 in the form of aso-called pigtail tip is arranged distally on the terminating housing13. The catheter 1 moreover comprises a lock 15. The function of thelock is to radially compress the pump head 10 when this is pulled intothe lock 15. The pump head 10 in this compressed condition for examplecan be subsequently led through an introduction lock (not represented inthe figures) and be implanted through this. The introduction lock forexample can be fixed at a puncture location on or in the body of apatient, in order in this manner to likewise support the catheter 1 atthis location. The document EP2399639 A1 is referred to in this context.

This catheter as part of a blood pump arrangement 16 is represented inan implanted condition in a greatly schematic manner in FIG. 2. What isshown is the use or application of the catheter 1 and the blood pumparrangement 16, with which the drive shaft 2 of the catheter 1 isconnected via the coupling element 5 to a corresponding coupling element17 of a drive motor 18 of the blood pump arrangement 1, in arotationally fixed manner (but axially displaceable manner, seedescription concerning FIG. 12). The drive motor 18 is designed toproduce high rotation speeds in a region between 10,000 and 40,000revolutions per minute.

As is shown in FIG. 10, a functional element which is designed as a pumprotor 20 is connected in a rotationally fixed manner to a distalend-piece 19 of the drive shaft 2. The pump rotor 20 is arranged withinthe pump casing 11 which in this embodiment example is designed suchthat it can be brought from a radially expanded condition into aradially compressed condition. This for example can be effected with thehelp of a lock 15 or the introduction lock mentioned above, preferablyby way of the pump casing 11, whilst being subjected to a (tensile)force acting towards the proximal end 8 of the catheter, being at leastpartly pulled into the respective lock and thereby being compressedalong a radial direction running transversely to the longitudinaldirection. The pump casing 11 can accordingly be brought from thecompressed into the expanded condition by way of a reverse force. Thedocument 2399639 A1 is also referred to here.

With the application of the pump arrangement 2 which is represented inFIG. 2, the catheter 1 with its distal end 9 in front, is insertedthrough a puncture location 21 into the body of a patient in its femoralartery 22 and is pushed along this via the aortic arch 23 into the leftventricle 24 of the heart 25. The pump casing 11 is thus positioned inthe left ventricle 24 such that it is supported by the support element14 on an inner wall 26 of the left ventricle 24, and the downstreamtubing 12 runs through the aortic valves 27 into the aorta 28. The bloodwhich is driven by the pump rotor 20 and which flows out of the pumpcasing is thus led through the downstream tubing 12 into the aorta 28.The proximal end 8 of the catheter 1, the proximal end-piece 3 of thedrive shaft 2 as well as the drive motor 18 are arranged outside thebody.

In this embodiment example, an (axial) total length or the catheter andan (axial) total length of the drive shaft 2 are in each case about 150cm (corresponding to an implantable length of about 140 cm), an (axial)total length of the distal end 9 of the catheter (including pump head 12and support element 14) is about 13.5 cm, in order to permit thisapplication. The flexibility or the pliability of the catheter 1, thusin particular of the drive shaft 6, the sleeve 6 and the sheath 7 are solarge that the catheter 1 can be implanted and operated, as has beendescribed above. For this, these components must be able to beelastically curved by 180° at least within the distal end 9 of thecatheter, with the typically radius of curvature R of the aortic arch 23of about 30 mm, as is shown in FIG. 2, without plastic deformation, inparticular of the drive shaft 2 thereby occurring.

As is shown in FIGS. 4 and 6, the drive shaft 2 is designed as a hollowshaft and comprises a cavity 29 extending axially within the drive shaft2, in order to achieve a high pliability of this drive shaft 2. Thecavity 29 extends along the total length of the drive shaft 2. Thiscavity 29 however is completely filled out with a reinforcement material30, a co-called core, at least within the roughly 4.5 cm long distalend-piece 19 of the drive shaft, see FIGS. 6, 9 and 10 and theassociated description further below, in order here to achieve anadequate stiffness and oscillation stability of the drive shaft 2 or ofthe distal end-piece 19 of the drive shaft.

The drive shaft 2 comprises a multitude of coaxial windings 31, 32 whichrun spirally around the cavity 29 of the drive shaft 2, in order toconvert torsion and bending stresses into axial tensile and compressivestresses. The windings 31, 32 are arranged in two coaxial layers 33, 34which is to say plies, of the drive shaft 2, wherein the windings 31 arearranged co-radially (with the same winding radius) within the innerlayer 33, and the windings 32 are arranged co-radially within the outerlayer. The windings 31 of the inner layer 33 have an opposite windingdirection compared to the windings of the outer layer 34, so thattensile and compressive stresses can be compensated between the layers.In the shown example, the drive shaft in the inner layer 33 comprisesfour wires 35 which are wound coaxially and co-radially around thecavity 29, and in the outer layer 34 five wires which are woundcoaxially and co-radially around the cavity, wherein axially adjacentwindings 31 of the inner layer mutually contact, but axially adjacentwindings (winding packet of five wires in each case) 32 of the outerlayer however do not mutually contact (in each case given an alignmentof the drive shaft which is free of curvature), but have an axialdistance of about 0.03 mm. An outer diameter d_(a) of the drive shaft inthe present example is about 0.88 mm and an inner diameter d_(i) about0.28 mm. The wires have a circularly round cross section with a diameterof about 0.15 mm. In the present example, the peripheral direction ofthe windings 36 of the outer layer 34 is counter to the designatedrotation direction of the drive shaft 2 for the (proximal) delivery ofblood.

Here, this rotation direction corresponds to the clockwise direction(defined for a viewing direction from the proximal to the distal end ofthe drive shaft). The torque to be transmitted in this case leads to theouter layer tending to contract and shorten. Since the inner layer 33has an opposite tendency due to its opposite winding direction, thesetendencies advantageous largely cancel each out. Basically, this mutualcompensation can also be achieved in the reverse case, when specificallythe winding direction of the outer layer corresponds to the rotationdirection and the winding direction of the inner layer is opposite tothe rotation direction of the drive shaft.

The wires 35, 36 of the drive shaft 2 consist completely of an alloy,which as alloy components contain about 35% by weight of nickel, about35% by weight of cobalt, about 20% by weight of chromium and about 10%by weight of molybdenum. These alloy components of the alloy can in eachcase also be greater or smaller by up to 3% by weight, or greater orsmaller in each case by up to 2% by weight. With regard to the alloy, inthis example it is particularly the case of 35NLT®, but it could just aseasily be the case of MP35N®. The weight component of iron in the wiresis thus less that 1% by weight and the weight component of titanium isless than 0.1% by weight. The alloy and the windings 31, 32 of the driveshaft are manufactured or formed amid the application of highcold-forming and work-hardening. In this example, a non-rusting,austenitic steel according to the material number DIN 1.4310(X10CrNi18-8) is selected as a reinforcement material 30 for stiffeningthe drive shaft 2. Alternatively, any other material which fulfils thedemands specified further above in this context could also be selectedas a reinforcing material.

The sleeve 6 is represented in FIGS. 7 and 8, which in the shown exampleis designed as a bearing coil with a multitude of windings 37, whereinthe windings 37 of the bearing coil run around the drive shaft 2 in theaxial direction in the manner of a spiral. In the present example, thebearing coil is given by a wound-on flat tape 38. The flat tape 38 has awidth B (measured axially) which is larger than the thickness D(measured radially) by a factor of about 6. In the present example, thewidth B of the windings 37 is 0.6 mm and the thickness D of the windings37 is 0.1 mm. The windings 37 are moreover angled which is to say tiltedas little as possible relative to the longitudinal axis L of the bearingcoil (in the straight condition without a curvature of the bearingcoil), where possible by less than 5°, so that an inner surface 39 ofthe sleeve 6 which is formed by the windings 37 is as cylindrical aspossible or forms as cylindrical as possible part-surfaces. Moreover,the lateral edges 54 of the flat tape are preferably as rounded aspossible, with a radius of curvature r_(k) of about 0.04 mm. The radiusof curvature r_(k) of the edges 54 is preferably more than 0.04 mm.Moreover, an inner diameter D₁ of the sleeve 6 is about 1 mm and anouter diameter D_(A) of the sleeve about 1.2 mm and has a gradient/pitchof about 0.7. The sleeve 6 or the flat tape 38 in this example consistsof the same alloy as the wires 35, 36 of the drive shaft 2, thus here of35NLT®, but could however also be manufactured of another one or thematerials which are mentioned for this.

The drive shaft 2 and the sleeve 6 could also consist of materials otherthan the alloys mentioned here. The drive shaft 2 is preferablymanufactured from the same material as the sleeve 6. Moreover, a surfaceof the drive shaft 2 can have a roughness RZ of about 0.6, by whichmeans surprisingly a particularly good wear resistance is achieved.Surprisingly good wear characteristics and thus a high operationalreliability can be achieved by way of these measures which are quitesimple to implement.

A longitudinal section through the axial section of the catheter 1 whichis indicated at Y in FIG. 1 is represented schematically in FIG. 9. Inthis section, the catheter 1 comprises bearing elements 40, 41, 42 whichare arranged proximally to the pump rotor 20, for the radial and axialmounting of the drive shaft 2.

The arrangement and design of these bearing elements 40, 41, 42 ismatched to the pump rotor 20 of the catheter 1 which is shown in FIG.10. This pump rotor 20 has a blading 43, whose configuration, design andpitch angle are configured for delivering the blood proximally (proximaldelivery direction, i.e. in the direction of the proximal end of thecatheter). The bearing meats 40 and 41 form a thrust bearing 44 which isarranged proximally to the pump rotor 20 (The bearing element 41 is afirst thrust bearing element of the thrust bearing 44, and the bearingelement 40 is a second thrust bearing element of the thrust bearing 44).The thrust bearing 44 on account of the design and arrangement of these(thrust) bearing elements 40, 41, is designed to counteract a distallydirected axial displacement of the drive shaft 2 (caused by the proximaldelivering effect of the pump rotor 20). Axial bearing forces actingmainly act upon the drive shaft 2 as tension forces on operation of theblood pump arrangement in this manner.

The (first) bearing element 41 is preferably designed in an annularmanner and is connected to the drive shaft 22 in a rotationally fixedmanner, for example by way of crimping. The (second) bearing element 40,just as the bearing element 42, in contrast is fixedly connected to thesleeve 6 and to the sheath 7. The bearing elements 40, 41 have annularsliding surfaces 45 and 46 respectively which face one another and whichblock an axial displacement of the drive shaft 2 in the distal directionin the case of a mutual contacting, The sliding surface 46 of the(first) bearing element 41 has a profiling, see FIGS. 13 and 14 and theassociated description below, by which means the formation of a stablelubricant film between the two sliding surfaces 45, 46 is encouraged,and basically a design of the thrust bearing 44 as a hydrodynamicsliding bearing is rendered possible. The lubricant film which is to saythe hydrodynamic bearing in this example is formed with the lubricantwhich is described further below. The bearing element 40, as also thebearing element 42, is moreover designed as a radial bearing element ineach case with a sliding surface which faces the drive shaft 2, isdesigned in a cylindrical manner and is arranged coaxially to therotation axis of the drive shaft 2.

Moreover, as is to be recognised in FIG. 9, the drive shaft 2 isreinforced by the reinforcement material 30, in the axial sections, inwhich it distally exits from the sleeve 6 which is to say is mounted bythe bearing elements 40, 41, 42.

A longitudinal section through the axial section of the catheter 1 whichis characterised by the reference numeral Z in FIG. 1 is schematicallyrepresented in FIG. 11, and this in particular includes the terminatinghousing 13 which is adjacent the pump casing 11. The terminating housing13 is designed in a tubular manner and comprises a distal bearingchannel 47 and a bearing element 47 which is arranged therein, for theradial mounting of the distal end-piece 19 of the drive shaft 2. Thecavity 47 in particular is dimensioned sufficiently large, in order topermit axial compensation movements of the drive shaft 2.

A longitudinal section through the proximal coupling module 4 shown inFIG. 1 is represented schematically in FIG. 12, said coupling modulecomprising a proximal bearing channel 49 for the proximal end-piece 3 ofthe drive shaft 2, wherein the proximal end-piece 3 of the drive shaft 2runs axially through the bearing channel 49 and projects axially out ofthe proximal coupling module 4. A bearing element 50 for the radialstabilisation or mounting of the proximal end-piece 3 of the drive shaft2 is arranged in the bearing channel 49. The sleeve 6 extends axiallythrough this bearing element 50 up to its proximal end. The bearingelement 50 in this embodiment has the function of radially stabilisingand supporting the sleeve 6 from the outside. In an alternativeembodiment, the sleeve 60 does not run through the bearing element 50,but ends (coming from the distal side) at the distal end of the bearingelement 50. In this case, the bearing element 50 for example is designedas a sliding bearing or as a roller bearing. The proximal end-piece 3can be stiffened by the reinforcement material 30, just as the distalend-piece 19, in particular in the axial sections, in which the driveshaft exits out of the bearing channel 49 or is mounted by the bearingelement 50. The bearing elements 40, 41, 42, 48 and 50 preferablyconsist of zirconium oxide, preferably in the form stabilised withyttrium, of aluminium oxide, of a ceramic or of the same materials asthe wires 35, 36 of the drive shaft 2.

The coupling housing 4 moreover comprises channels 51 for the feed anddischarge of the lubricant, Wherein the channels are connected in afluid-leading manner to the bearing channel 49 as well as to anintermediate space between the sleeve 6 and the drive shaft 2. Accordingto the sixth aspect of the invention, an intermediate space orintermediate gap between the drive shaft and the sleeve is filled with alubricant which is biocompatible and preferably also physiological. Thelubricant is biocompatible and in this example is the case of distilledwater, but it could also be a physiological saline solution or glucosesolution.

The coupling element 5 of the drive shaft 2 is designed as rigidly aspossible and is connected to the proximal end-piece 3 of the drive shaft2 in a manner fixed with regard to rotation, traction and compression.The coupling element 5 of the drive shaft as well as the couplingelement 17 of the drive motor 18, which in this example is designed as areceiver for the coupling element 5, comprises axial sliding surfaces 52and 53 respectively, which correspond to one another, for forming arotationally fixed, but axially displaceable connection. These slidingsurfaces run parallel to the longitudinal axis of the respectivecoupling element 5 and 17 respectively and do not change their shapealong the longitudinal axis of the respective coupling element 5 and 17respectively. With this example, with regard to the coupling element 5of the drive shaft 2 it is the case of a square end.

The sheath 7 can consist completely or at least regionally of a plastic,for example of polyurethane, in particular of a carbothane or aurethane. The sheath preferably has a metal reinforcement, which forexample can consist of the alloy which is suggested for the drive shaft,thus for example of MP35N®.

FIGS. 13 and 14 in each case show a schematic perspective representationof an embodiment example of the first bearing element 41 of the thrustbearing 44 which is shown in FIG. 9. The sliding surface 46 of therespective bearing element 41 comprises a profiling 55, so that the twosliding surfaces 45, 46 with an interaction with the lubricant form ahydrodynamic sliding bearing, by which means a wear volume of thesliding surfaces 45, 46 or of the two bearing elements 40, 41 can besignificantly reduced. In the embodiments represented here, theprofiling 55 of the respective sliding surface 46 comprises severalprominences 56 and recesses 57. In the example represented in FIG. 13,there are exactly 12 prominences and 12 recesses, in the example shownin FIG. 14 there are precisely 8 prominences and 8 recesses, wherein theprominences 56 and recesses 57 in each case are arranged uniformlydistributed over the sliding surface 46 along a peripheral direction orcircumferential direction (indicated in each case by a arrowcharacterised by U in the figures) of the respective sliding surface 46and are designed as an alternating sequence of ribs and grooves.

These ribs and grooves extend in each case from an inner edge 58 of therespective sliding surface 46 which faces the drive shaft 2, up to anouter edge 59 of the respective sliding surface 46 which is away fromthe drive shaft 2. In the example represented in FIG. 13, the ribs ineach case have a height (this corresponds to the depth of the respectivelaterally adjacent groove) of about 0.06 mm and an average width(measured in the peripheral direction U) of about 0.2 mm. In the examplerepresented FIG. 13, the prominences 55 which are designed as ribs ineach case have a maximal height of about 0.1 mm, wherein each prominencehas a leading surface 60 and a trailing surface 61, wherein the leadingsurface 60 advances with respect to the trailing surface 61 given arotation of the bearing element 41 in the designated rotation directionalong the peripheral direction U (in the clockwise direction given aviewing direction to the distal end 9 of the catheter 1).

This leading surface 60 is inclined or bevelled with respect to thelongitudinal axis of the bearing element 41, in a manner such that theprominence 56 reduces or tapers upwards (i.e. in the direction of theopposite sliding surface 45 of the second hearing element 40, thus inthe distal direction in the present example). Basically, thus in anyother embodiment examples of profilings of the bearing element 41, amore uniform bow wave formation of the lubricant can be achieved, and byway of this a more stable lubricant film can be formed, with suchinclined which is to say bevelled leading surfaces 60. On its respectiveupper side 62, each of the prominences 56 has an average width (measuredin the peripheral direction U) of about 0.3 mm, wherein the width of theprominence 56 increases in the radial direction. An average width(measured in the peripheral direction U) of the grooves 57 in thisexample is about 0.1 mm, wherein the width of the grooves also increasesradially outwards. The embodiments which are shown in FIGS. 13 and 14can be manufactured for example by way of a (cutting) laser.

The dependency between the material characteristics yield point, tensilestrength, elongation at break and cold work-hardening degree, based onthe details of the manufacturer Fort Wayne Metals, is represented withthe example of the material 35NLT in FIGS. 15 and 16. By way of thisexample, it is shown that different heat-treatment conditions andwork-hardening degrees of a material can generally lead to verydifferent material characteristics.

For example, if the drive shaft 2 and/or the sleeve 6 of the embodimentexample shown in FIGS. 1 to 15 consist of 35NLT, then the work-hardeningdegree of this material is preferably at about 35 to 70%, particularlypreferably at 50% to 60%, so that here a tensile strength of about 2000to 2200 Mpa, for example 2068 MPa is achieved, and a elongation at breakof 3.5% is not fallen short of. In the foregoing disclosure, it will beunderstood that the term “about” should be taken to mean±20% of thestated value, as is known in the art.

LIST OF REFERENCE NUMERALS

1 catheter

2 drive shaft

3 proximal end-piece of the drive shaft

4 coupling module

5 coupling element of the drive shaft

6 sleeve

7 sheath

8 proximal end of the catheter

9 distal end of the catheter

10 pump head

11 pump casing

12 downstream tubing

13 terminating housing

14 support element

15 lock

16 blood pump arrangement

17 coupling element of the drive motor

18 drive motor

19 distal end-piece of the drive shaft

20 pump rotor

21 puncture location

22 femoral artery

23 aortic arch

24 left ventricle

25 heart

26 inner wall

27 aortic valve

28 aorta

29 cavity

30 reinforcement material

31 winding of the drive shaft

32 winding of the drive shaft

33 coaxial layer of the drive shaft

34 coaxial layer of the drive shaft

35 wire of the drive shaft

36 wire of the drive shaft

37 winding of the sleeve

38 flat tape

39 inner surface of the sleeve

40 bearing element

41 bearing element

42 bearing element

43 blading

44 thrust bearing

45 sliding surface

46 sliding surface

47 bearing channel of the terminating housing

48 bearing element

49 bearing channel of the coupling module

50 bearing element

51 channel for the lubricant

52 sliding surface

53 sliding surface

54 edge

55 profiling

56 prominence

57 recess

58 inner edge

59 outer edge

60 leading surface

61 trailing surface

The invention claimed is:
 1. A flexible catheter comprising: a driveshaft; a sleeve surrounding the drive shaft; and a sheath surroundingthe drive shaft and the sleeve, wherein the drive shaft, the sleeve, andthe sheath are configured to be flexible, and the drive shaft, at aproximal end of the drive shaft, has a coupling element for connectingthe drive shaft with a drive motor, and the drive shaft consists atleast partially of an alloy which comprises at least 10% by weight ofchromium, nickel and cobalt, wherein the sleeve is configured as abearing coil with a plurality of windings, each winding of the pluralityof windings rotating helically around the drive shaft in an axialdirection.
 2. The catheter according to claim 1, wherein the alloycomprises at least one of: (i) 30%-40% by weight nickel, (ii) 30%-40% byweight cobalt, and (iii) 15%-25% by weight chromium.
 3. The catheteraccording to claim 1, wherein the alloy has a tensile strength between1800 N/mm² and 2400 N/mm².
 4. The catheter according to claim 3, whereinthe sleeve is at least partially made from the alloy that has thetensile strength between 1800 N/mm² and 2400 N/mm².
 5. The catheteraccording to claim 1, wherein the sleeve is at least partially made of asame material as the drive shaft.
 6. The catheter according to claim 1,wherein the bearing coil comprises a wound ribbon.
 7. The catheteraccording to claim 6, wherein an axially measured width of turns of thebearing coil lies in a range of 0.36 mm to 0.84 mm or that a radiallymeasured thickness of the turns of the bearing coil lies in a range of0.06 mm to 0.14 mm.
 8. The catheter according to claim 6, wherein thewindings of the bearing coil, when in a straight condition withoutcurvature, has an axial tilting of less than 5° relative to the axialdirection.
 9. The catheter according to claim 6, wherein lateral edgesof the ribbon are rounded.
 10. The catheter according to claim 9,wherein the lateral edges of the ribbon have a curvature radius of 0.04mm or more.
 11. The catheter according to claim 1, wherein a slope ofthe bearing coil lies in a range of 0.43 to 0.98.
 12. The catheteraccording to claim 1, wherein an inner diameter of the sleeve lies in arange between 0.6 mm and 1.4 mm or an outer diameter the sleeve lies ina range of 0.72 mm to 1.68 mm.
 13. The catheter according to claim 1,wherein a surface of the drive shaft has a roughness RZ between 0.01microns and 1 micron.
 14. A blood pump assembly with a catheter,comprising: a blood pump; a drive shaft; a sleeve surrounding the driveshaft; and a sheath surrounding the drive shaft and the sleeve, whereinthe drive shaft, the sleeve, and the sheath are configured to beflexible, and the drive shaft, at a proximal end of the drive shaft, hasa coupling element for connecting the drive shaft with a drive motor,and the drive shaft consists at least partially of an alloy whichcomprises at least 10% by weight of chromium, nickel, and cobalt,wherein the sleeve is configured as a bearing coil with a plurality ofwindings, each winding of the plurality of windings rotating helicallyaround the drive shaft in an axial direction.
 15. The blood pumpassembly of claim 14, wherein the blood pump assembly further comprisesa drive motor, wherein there is a non-rotatable and axially displaceableconnection between the drive motor and the coupling element of the driveshaft.
 16. The blood pump assembly of claim 14, wherein the alloycomprises at least one of: (i) 30%-40% by weight nickel, (ii) 30%-40% byweight cobalt, and (iii) 15%-25% by weight chromium.
 17. The blood pumpassembly of claim 14, wherein the alloy has a tensile strength between1800 N/mm² and 2400 N/mm².
 18. The blood pump assembly of claim 14,wherein the sleeve is at least partially made of a same material as thedrive shaft.